Monitor



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SEARCH RGON C. PROTZE MONITOR Feb. 8, 1938. 2,107,425

Filed Aug. 20, 1936 KEYED WAVE FROM TRANSMITTER FAOM OUTPUT 0F TELEGRAPH REEE/I EI? ATTO R N EY Patented Feb. 8, 1938 PATENT OFFICE MONITOR Curt Protze, Berlin, Germany, assignor to Telefunken Gesellschaft fiir Drahtlose Telegraphic m. b. H., Berlin, Germany, a corporation of Germany Application August 20,

1936, Serial No. 96,980

In Germany July 13, 1935 3 Claims.

In the wireless communication it is often desirable for the telegraph operator to be able to hear his own telegraph signals as produced in the transmitter in order to be able to control the 6 working of his transmitter. For this supervision it is necessary to be sure that the high frequency power is actually being sent out. It should be kept in mind that this could not be readily ascertained where the control arrangement or moni- 1 toring means is placed directly in the keying circuit, since it is possible that failure may take place within the individual stages of the transmitter and not be noticeable to the operator.

Where a supervisory control for the entire transmitter is required there exists the disadvantage that the controlling volume, i. e., the monitoring signals fluctuate to a high degree unless means to counteract this fluctuation are provided. In many cases the transmitter is not always operated with the same power, since at resumption of communication a high power is used for sending to permit the transmitter easily to assume its proper operating state. Thereafter the power is reduced to a point just suflicient to retain the volume necessary for communication.

Not only is the fluctuation in the volume of the transmitter of great inconvenience to the telegraph operator, but eventually if the volume becomes too large it will endanger the hearing of 0 the operator, and it will also not be possible for the latter to hear the softer signals of the opposite station with suflicient clarity directly after his hearing has been jeopardized on account of too large a volume. For this reason an automatic volume control is greatly desirable.

The arrangement heretofore used was such that the high frequency obtained from the transmitter has been detected, and the direct potential so obtained has been utilized as plate potential of a 40 tube arranged as tone frequency generator. However, in this case a sufficiently constant volume was not attainable since the plate potential of the tone frequency generator and hence the amplitude of the tone produced varies with the energy of the transmitter to be controlled.

An automatic volume control such as known for instance in broadcast reception could be used. However, this involves difiiculties since for commercial communication several other requirements must be fulfilled. It is not advisable to use special control tubes such as hexodes in telegraphy systems for instance, since owing to the desire of reducing the number of spare tubes to a minimum, the number of different types of tubes in a receiver should be as small as possible. In

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addition it should be borne in mind that for commercial communication, tubes having different over-all dimensions are used whereas modern multiple electrode tubes as used in receivers, are not as yet manufactured in the commercial transmission form. It would obviously be possible to avoid such special tubes and not to avail oneself of the advantages thereof, but the circuits hitherto known have the disadvantage that the control arrangements are sensitive to variations in the operating voltages, and that even the tubes of the same type diifer as to their characteristics, so that therefore the position of the lower bend of the characteristic is not established with sufllcient accuracy.

In accordance with the present invention, the constant volume in an audible control device for transmitted telegraph signals is attained in that the high frequency derived from the transmitter and then detected is applied to the grid of a tube serving as control organ or element for the receiving indicator, whereby the grid potential of said tube is prevented from becoming more positive under the influence of a counter potential despite an increase in the detected positive potential,

said counter potential being produced by the grid current at an ohmic resistor placed in the grid lead. Thepinvention may be put into practice by connecting the tube serving as control organ in the plate circuit of a low frequency generator,

and negatively biasing the grid of said control tube to such a degree that it will be blocked when the detected high frequency fails, thereby,-stopping the generator owing to a cutting off of the plate potential.

This arrangement will now be elucidated with reference to the single figure in the drawing wherein I have illustrated one embodiment of my monitoring circuit. The keyed high frequency is supplied from the transmitter across condenser C to the detector tube I whereby said high frequency may be derived from the antenna or from an intermediate circuit for instance, although as is obvious, it may also be inductively transmitted to coil Sp. The high frequency potential appearing at the ends of coil Sp will be detected in tube l, which by the way, may be a single grid tube to avoid increasing the number of types of tubes, the grid of said tube being connected to the cathode or anode.

There appears at the terminals of resistor W a direct-current potential of the rhythm of the keyed signals, the value of which depends upon the power to which the transmitter is adjusted to send out. The time constant of the circuit consisting of resistor W and condenser C1 is sufficiently short to avoid distortion of the signals at the highest telegraph speeds. The produced direct potential is applied to the grid of tube 2 in such-manner that it opposes the negative bias of battery V. During the pauses of the operator's own transmitter no voltage exists at resistor W so that only the biasing potential V is efiective, and which is just sumcient to block the tube 2. Consequently owing to the then existing high direct current resistance of tube 2, the plate potential applied between -A and +A will be substantially distributed over the impedance of tube 2, thus preventing the tube 3 from oscillating owing to insufiicient plate potential so that no tone can be heard in the head piece T. But the receiver can then be heard across the conductors shown.

If operators own transmitter is being keyed, a direct potential appears at W imparting to the grid of tube 2 a more positive bias thereby reducing its direct current resistance. Then tube 3 receives plate potential and oscillates. Up to this point the arrangement does not offer any advantage in reduction of loud signals in the monitors phones in the presence of high amplitude telegraphy, since for higher direct potential at W, the plate potential on 3 likewise increases. This is avoided however, in the present invention by utilizing the condition that the grid current flowing in tube 2 produces in resistor R placed in the grid circuit a negative, and hence opposing potential. This opposing potential as is obvious, is also produced at W, but in view of the aforementioned short time constant W is but a low ohm resistor, whereas the value of R is approximately equal to 500,000 ohms.

n the other hand, it will not be possible to maintain a short time constant by decreasing 01 while providing a large value for W, since C1 is to represent a sufiicient short circuit as regards high frequency. If, therefore, the potential appearing at W exceeds the biasing potential V so that a positive bias exists at tube 2 producing a grid current, this increasing positive potential at W owing to the opposing potential at R causes a but very slightly higher positive potential at the grid of tube 2. Moreover, in view of this fact the direct current resistance of tube 2 and hence the plate potential at tube 3 will be constant, and therefore also the volume will have the same value despite varying high frequency intensity.

The advantage of the arrangement resides in that with few auxiliary means it is possible to obtain a constant volume throughout a very wide signal amplitude range, and that changing the controlling tube 2 owing to the relatively constant grid current development, does not cause a change in the operating condition.

As already pointed out, the range of constant volume begins only when grid current flow begins, i. e., when the negative biasing potential V is overcome. However, this is no disadvantage since for instance at a fluctuation of the transmitter power at the ratio of for instance 1:1000 (for instance between 20 w. and 20 kw.) and at a corresponding fluctuation of the voltage amplitude at the ratio of 1:33, the audible control device can be coupled to the transmitter in such a way that at the lowest power of 20 w. which appears, grid current starts already.

Furthermore the feedback of tube 3 can be so dimensioned that it still remains in the non-oscillating state at low plate potentials. Finally, by causing the tube 3 to oscillate at excessive potential, the constancy of the volume can be still further enhanced.

I claim:

1. In a device for producing monitoring signals indicative of the operativeness of a transmitter and for controlling the intensity of the signals produced, an oscillator including an electron discharge tube having electrodes connected in oscillation producingcircuits, one of which circuits includes a source of potential sufiicient to produce oscillations in said tube and circuit, a second electron discharge device having its impedance connected with said one of said circuits and source of potential to control the value of the potential applied by said circuit to one 01 said electrodes, said discharge device having a control grid and a circuit therefor including means for normally biasing said device to a point at which said second device impedance is high and oscillations are cut off in said first tube-and circuit, a resistance connected with said control grid, rectifying means connected with said resistance for producing a potential therein opposing the normal potential applied to said control grid whereby oscillations may be produced in said oscillation generator tube and circuits, means for impressing Wave energy to be monitored on said rectifier, and additional means for producing an additional potential drop which opposes said potential drop produced in said resistance when direct current flows in to the grid of said second named device.

2. In a system for producing indications of the presence of wave energy in the output of a transmitter and maintaining said indications of substantially constant amplitude, an oscillator comprising an electron discharge device having its electrodes connected in oscillation producing circuits, tube impedance means and a source of potential connected in one of said circuits of said device for charging an electrode of said device to a potential relative to its cathode at which said device is substantially cut off, and oscillations are not produced in said tube and circuits, rectifier means energized by and responsive to wave energy to produce a. controlling potential, means connecting said rectifier to said tube impedance means to control the impedance thereof, in the presence of said produced potential to increase said potential to which said electrode is charged relative to said cathode to cause said device and circuits to produce oscillations, additional means for producing a potential which opposes said first named controlling potential in the presence of oscillations of substantial amplitude in said device and circuits, and an indicator coupled to said.

device.

3. In a device for indicating the presence of the wave energy sent out from a transmitter and for producing indications thereof of substantially constant amplitude in an indicator, an electron discharge device having an anode, a cathode, and a control grid connected in oscillation producing circuits, one of which includes a source of potential, a second electron discharge device having an anode and a cathode connected in said last named circuit, said second device having a control grid, a source of potential for normally biasing said control grid negative relative to said cathode to increase the impedance of said second device to lower the potential on the electrodes of said first named device to prevent the production of oscillations in said first named device and circuits, a rectifier having input electrodes excited by wave energy from the transmitter and having output electrodes connected with a resistance in circuit of said second named device for produc ing a potential in the presence of grid current therein which opposes the potential produced in the resistance connected with the output of said rectifier and an indicator coupled with said first 5 device.

CURT PRO'I'ZE. 

